The Sherlock Holmes star was last seen in Marvel's Avenger's: Age of UltronGetty Images

Iron Man star Robert Downey Jr, who has had a troubled past with substance abuse, received an unexpected Christmas gift on 24 December as he was granted pardon by California Governor Jerry Brown for a conviction and jail in a drug and weapon case 20 years ago. In June 1996, Downey Jr was stopped for speeding on the Pacific Coast Highway in Los Angeles County and authorities found cocaine, heroin and a pistol in his vehicle.

"He has lived an honest and upright life, exhibited good moral character, and conducted himself as a law-abiding citizen and has paid his debt to society and earned a full and unconditional pardon," said a proclamation from Brown's office. The statement added that while the pardon does not erase records of a conviction, it does restore voting rights and is a public declaration that the person has remained out of trouble and demonstrated "exemplary behaviour".

The Oscar nominated star, who is currently Hollywood's highest paid actor, has been in and out of jail and rehabilitation centres for drug abuse over the years. In the 1996 case, he spent one year and three months in jail, two years on parole and nearly three years on probation for his convictions, according to the governor's office, CNN reported.

Downey has maintained that he has been drug-free since July 2003 and has credited his wife with helping him kick his drug and alcohol habits.

The star reportedly had his first experience of drugs when he was only six years old after his father, also a drug addict, let him try a cannabis joint. The actor claims he started indulging in these activities with his father as an emotional bonding experience.

The Sherlock Holmes star, who was last seen in Marvel's Avenger's: Age of Ultron, will be seen reprising the character of Tony Stark/Iron Man in 2016 in Captain America: Civil War.

The actor was one of 91 people who was granted clemency by the governor for past crimes, most of them minor drug offences that are no longer felonies under California law. Brown has issued hundreds of pardons in each of his four terms in office, mostly around the holidays.